Capacitor switch



April 6, 1948. R. c. LONGFELLow 2,439,255

cAPAcIToR SWITCH Filed Sept. 9 1942A In ve ntor:

Richard C. Lon gfel low,

Patented Apr. 6, 1948 CAPACITOR SWITCH Richard C. Longfellow, Schenectady, N. Y., assig-nor to General Electric Company, a corporation of New York Application September 9, 1942, Serial No. 457,776

8 Claims. 1

My invention relates to reactance devices and more particularly to such devices for use at short wave lengths.

In my United States Letters Patent No. 2,412,160, granted December 3, 1946, entitled Directive radio systems, and assigned to the same assignee as my present application, I have disclosed a directive antenna array in which the direction of the axis of directivity of the array may be altered by changing the transmission lines leading to the array. That is, different portions of the array are supplied alternately through rerespective transmission lines, the lines through which no energy is supplied at anytime being rendered inoperative. Means is employed whereby the energy is supplied through the various lines in rotational sequence, the arrangement being such that the axis of directivity of the array is rotated by this rotation of the lines.

This means comprises means for varying the impedance across each of the lines, at a desired point thereof, between very high and low values to render the line either operative or inoperative as desired. To this end, stub transmission lines are connected at said points respectively and extend to a rotating reactance device whereby the impedance across the opposite end of such stub lines is varied in rotational sequence between such low and high values, the length of the stub lines being such that the change in impedance of the reactance device is translated to the respective transmission line to Vary its condition of operation.

This reactance device comprises a condenser having a motor driven rotor electrode which cooperates in sequence with each of a plurality of stator electrodes. The rotor is grounded and connected to one conductor of each line while each stator electrode is connected to the opposite conductor of the respective line whereby the impedance between said conductors of the different lines is varied in rotational sequence by rotation of said motor driven electrode.

My present invention has for its object to provide an improved reactance device, which, while not limited thereto, may be employed for the purposes above explained and which has longer life and assures greater reliability of the system.

Another object of my invention is to provide a reactance device of such construction as to reduce the flow of currents through the rotating shaft thereof and hence through the bearings of the motor by which the shaft is driven. In this way injury to the bearings of the motor produced by such currents is avoided.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, however, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in which Fig. 1 shows a partially sectioned elevation of a switch constructed in accordance with my invention and Fig. 2 is an end View of a portion thereof.

In the drawing I have indicated at I0 a reactance device having a plurality of stator members II and a rotatable member I2 arranged for electrically controlling the currents flowing in a plurality of coaxial lines I3, here shown as four, the inner conductors 0f the lines being connected to the stator members I I. 'Rotation of the member I2 for switching of the high frequency currents carried by the lines I3 is effected by means of a motor I4 having a shaft I5 for supporting the member I2. The transmission lines I3 are connected to circuits, not shown, carrying high frequency currents, such as an antenna array, for example, and the capacitor switch I0 provides a means for rapid shifting of the order of energizing adjacent pairs of radiators of such an array for the purposes and in the manner disclosed in my above-mentioned copending application.

The fixed or stator members II may comprise one or more plates I6 having the general form of a sector of a circle and the rotor member I2 may comprise one or more conductor plates I'I, semicircular in shape as shown in Fig. 2, or of any other desirable shape such that the plates I'I are capacitively coupled to the adjacent plates I6. rThe individual plates I6 are held in spaced relation by means of the shoulder members I8 and a rod-like member I9 is provided for connecting the stators II with the inner conductor 2U of the transmission lines I3. Preferably, the plates I6, the shoulder members I8 and the rod member I9 are formed as a unitary structure. Conductors I9 and 20 may be connected together in any suitable manner, for example, as by threaded engagement with a connecting link 2I.

In order to hold rigidly the stator members II in spaced relation with each other, as well as to provide means for conductively connecting the outer conductors 22 of the coaxial transmission lines I3, a cylindrical metal casing or'housing member 23 is provided having a plurality of spaced openings through which the connection of conductor I9 with conductor 20 is effected, the tubular conductor 22 being secured to the houslmember .3 I,

Vand back .to the outer .conductor v22. .another-shunt path lthroug'h which Vthe currents ing 23 around such openings in any desirable manner, such as by brazing or soldering. Suitably shaped insulators are provided to surround the conductor IS in these openings, maintaining conductor I9 in a predetermined spaced relation with tubular member 22, and maintaining the shoulder members .I'B in spacedrelation with respect to the-housing 23,

In order to maintain the shaft I in a fixed position with respect to the inner edges of the plates I6, thereby to x the position of plates I'I with respect to plates I6, a metallic sleeve lmember 25 is welded to the frameiofrfmotor I4 .and bolted to an inwardly projecting portion 28 of housing 23, thus forming a closure member for the respective end of housing 23. pacitor switch of the type thus'far'described `is usually operated in a gaseous atmosphere fof controlled pressure, endlplates 2'I and 28 are providedV to close .the ends .of uthe casing 23 .and the sleeve `member 25, -gaskets 29 being ...provided to maintain `the enclosure -in a gas-tight condition,

.1V-For purposes which will Vbecome apparent, an

outer rotor Shaft-in thevformof a metallic tubular sleeve :30, surrounding shaft I5, is provided and-servesas-anelectrically conductive path be- .tweenplates =`I kdf capacitor switch I!) and .plate which forms with Vthe end wall "2e a groundingcapacitorforthe switch I 0,1the grounding capacitor having a'low capacitive reactance at the ffrequency of .the .current owing in the system.k I

In the .operation of the circuit thus A.far described, `the y.desired path .for the high v'frequency .currentsis between .theinner conductor '20 and outer return conductor .'22 of aparticular trans- .mission line I3. The-currents owalong the'inner conductor T through :the connecting conductor I 9, the stator-plates [6, .therotorplates I1, along the .tubular .member A-3`I), through the grounding capacitor plate 3l .to 'the wall 2B, thehousing A23, There is may flow. This .path goes from conductor 2'to the-memberf30 fas .described before. 7Instead of l.passing from Ythe Agrounding .capacitor .plate 3l to the housing i23, this shunt "current Vpasses to the-inner 4rotorshaft f5 on through the motor bearings 32150 tlieenclosing shield'25 and back through screws .2'9 to `the main housing 23 and theouter .conductor'22. Y

In Vthe presenceoflhigh .frequency currents of large magnitude in `the first circuit, the voltages induced iin the shunt circuit are of sufficient magnitude to .cause `the oil filmin the Vbearings 312 to break down Vandhigh .frequency currents of considerable .magnitude to flow in the shunt path. In `the presence of such currents, considerable arcing occurs between thebearing surfaces withresultant pitting ofthe surfaces. As a consequence,.after a veryshort'life, failure of the motor bearings results and the switch becomes inoperative.

Since a caspectively of a concentric transmission line, having a length equal to a quarter wave length of the wave having the operating frequency of the system. The end of this line remote from the bearings 32, that is at the left end of the shaft I5, is short circuited by a metal plug member 34 carried onshaft l5 and having shoulders for engaging'the end of sleeve Z3l). At the opposite end of the transmission line, the plate 3l is conductively connected to member 3B and extends parallel to the end-wall portion of the housing 23.

-In accordance with well-known transmissionilinetheory, the.s`hort circuit across the one end of the above described transmission line is inverted by the quarter wave length line to appear las'an-impedancefof 'lhigh value at the other end able insulating material, preferably a ceramic v bonded mica'insulating material, such as'Mycalex.

Also, the length of the shaft Vmember 32' is made equal to an electricalquarterwave-lengthof the high frequency current presentonthe lines I3.

Thus, thefinner shaft I5 andthe outershaft-member Eil form the inner and outer conductors reof the line. Thus, by this construction a large impedance is inserted yin the shunt path previously pointed out and is eiective to eliminate almost ventirely Acurrents iiowin'g inth'is shunt path.

In order wto remove lany currents which may still .tend to iiow through the motor bearings `32 becauselof inaccuracies in 'the 'length vofthe quarterwave transmission line or because of '-variation Ain the operating frequency vf the -vSystem, another'path 'inshunt to bearing 32 is Yprovided bymeans of the slip-ring securelyattached to the shaft I5 at the end 'of the insulating sleeve 33, andthe ybrush member 3S rconductively connec'te'd to'the wall '26 and bearing upon the slipring35. Theslip-ring 35 preferably iso'f'some good commutatormaterial, such as copper, 4and thelbrush member viifof a suitable brushmaterial, such asfcopper'oricarbon.

In the assembly of the lswitch, -fafter the slipring '35 has *been secured to the shaft I 5 Vand the sleeve 33 slipped over -the 'shaft into abutment with slip-ring 35,the sleeve l2'5,bearingthemotcr frame IQ, is bolted in place 'on the housing 23. 'The unit comprising the-outer Ashaft member l313, the disk 3|"andthe plates FI is thenslipped over the insulating 'sleeve l'33, after which 4vthe -short circuit `plug 34 Vis 'inserted land a bolt T31 -fused to hold Itheparts together'as Aa Vrigid structure. Before `the `stator 4members `I"I may `be placed in position, the shaft I5 'is :rotated to a position such ythat the 'plates I-I `lio not prevent 'the insertion vof a particularfstator member.

Itwill'thusibe' seen that thestructure described above provides Vla l'capacitor switch in `4which the motor "shaft 4of 'the 'unit is electrically isolated from high frequency currents, while mechanical rigidity 'of the'structurelismaintained. 'Bymeans 'of a 'quarteriwavefsection 'of the transmissionlline, a short circuit, atthe endo'f -theline remote from the bearing, `vis inverteditoiappearas ahighlimpedance in v series 'with the -s'hunt conductivev path which/includes 'the 'motor bearings 132. fBy the ruse .of this structure in valcapacitor switch remployed 'in Va signalling systemfoperating Vat va yfrequency of 400 megacy'cles, the ycurrent 'owing through the motor Ibearings-of the unit was vreduced froma value 'which rapidly vdestroyed the bearings toa value which caused nonfarm.

While I have 'described the transmission 'line comprising the'innerfshaft I 5 and thefoutersha'ft member 3% as havingalengthofr a quarter wave length, itwillbe'apparentitoithose skilled in the art that this length may be any multiple of a quarter wave length. *Whenthe lengthis ahalf wave length, the'plug'member SII'is'of somesuitable insulating material. `Thus,'a'.liighimpedance is connected across this remote end of :the Vline and the half wave lineis effectiveto cause this impedance to appear as a series impedance of high value in the above-mentioned shunt path.

While I have shown a particular embodiment of my invention, therefore, it will of course be understood that I do not wish to be limited thereto since various modifications may be made, and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a capacitance device having a conducting shaft, a rotating electrode supported by said shaft and separated therefrom by insulating means, said electrode being subjected to electromotive force relative to said shaft of short wave length, and a conductor extending along said shaft conductively connected to said electrode but insulated along its length from said shaft to form a transmission line, said line having a length equal to a quarter of a wave length, or multiple thereof, of said electromotive force, and the impedance across one end of said line being such relative to the length of the line as to reduce the liow of current in said shaft produced by reason of said electromotive force.

2. In combination, a capacitance device having a conducting shaft mounted in bearings, a rotor electrode supported by said shaft and separated therefrom by insulating means, said rotor being subject to electromotive force relative to ground, a conductor conductively connected to said electrode and extending along but insulated along its length from said shaft to form therewith a transmission line, said shaft and conductor having such length and the impedance therebetween relative to said length at the end remote from said bearings being such that a current flowing from said shaft through said bearings to ground is reduced by the impedance of said transmission line.

3. In combination, a capacitance device having a conducting shaft mounted in bearings, a rotor electrode supported by said shaft -and separated therefrom by insulating means, said rotor electrode being subjected to short wave electrometive force relative to ground and being grounded through impedance, and means to reduce the flow of current produced by said electromotive force from said rotor through said shaft and bearings to ground, said means comprising a conductor connected to said rotor and supported by and extending along said shaft in insulated relation thereto to form therewith a transmission line having-a length relative to a wave length of said electromotive force materially to increase the impedance between said rotor and shaft to said fiow of current.

e. In combination, a switch for high frequency current comprising fixed and rotatable members, means for enclosing said switch and for supporting said fixed member, means attached to said enclosing means and including a shaft for rotating said rotatable member, and means for preventing the iiow of current through said shaft to said enclosing means comprising a tubular member supported by and surrounding a portion of said shaft and forming therewith a transmission line, said rotatable member being conductively connected to said tubular member and being separated from said shaft by insulating means, said line being short circuited at one end and of such length that said short circuit appears as a high impedance connected in series circuit between said rotatable member and said enclosing means.

5. In combination, a switch for high frequency currents comprising fixed and rotatable members, means for enclosing said switch and for supporting said fixed member, means attached to said enclosing means and including a shaft for rotating said rotatable member, and means for preventing the ow of current along said shaft to said enclosing means comprising a tubular member surrounding a portion of said shaft and forming therewith a transmission line, said rotatable member being conductively connected to said tubular member and being separated from said shaft by insulating means, said line being short circuited at one end and of such length that said short circuit appears as a high impedance connected in series circuit between said rotatable member and said enclosing means, and reactance means of low value connected between said line at its other end and said enclosing means.

6. In combination, a reactance device for high frequency current comprising fixed and rotatable members, means for enclosing said device and for supporting said fixed member, means attached to said enclosing means and including a shaft for rotating said rotatable member, and means for preventing the iiow of current along said shaft to said enclosing means comprising a conductive member supported from a portion of said shaft and forming therewith a transmission line, said line being short-circuited at one of its ends and being connected to said enclosing means through a reactance at its other end, said line being of such length that said short circuit appears as a high impedance connected in series circuit between said rotatable member and said enclosing means.

7. In a capacitor switch for high frequency currents comprising fixed and rotatabe condenser plates, means including a shaft for rotating said rotatable plates, and a housing surrounding said plates and having means for supporting said shaft, said shaft and supporting means forming an undesired path for high frequency currents in parallel with said plates, means for preventing the flow of current through said path, said means comprising a metallic sleeve surrounnding a portion of said shaft aIld forming therewith a transmission line having a length equal to a quarter of a wave length at the frequency of said currents, said rotatable plate being con ductively connected to said sleeve at a point intermediate the ends thereof, and means for short circuiting said line at the end remote from said supporting means, said lline being effective to `invert said short circuit to appear as an impedance of large magnitude in said path.

8. The combination, in a capacitor switch for high frequency currents, of a housing, a stator member supported in said housing, a rotor member, said stator and rotor members forming a first conductive path for said currents, a rotatable shaft mechanically coupled to said rotor member, means for supporting said shaft in said housing, and means for preventing the flow of said currents from said rotor member through said shaft to said housing, said means comprising a tubular member conductively connected to said rotor and extending over said shaft and insulatingly spaced therefrom, said shaft and tubular member forming a transmission line having a length equal to a quarter wave length at the frequency of said currents, and impedance means of low value connected across said line at the 7 end remote `from said supporting means, .said line being eiective to invert said impedance to ap* pear as animpedance c); largevalue Qonnected in seriescircuitwth said rotor and said housing.

RICHARD C.l LONGFELLOW,

The following-references are of record ip the le of this patent:

Number 

